Bulb and capillary thermostats are known as remote temperature control units for controlling the temperature in water heaters, hot tubs, water beds, spas, coffee and hot drink dispensers and the like.
The actuator assembly of a thermostat includes a head assembly, a bulb, and a capillary interconnecting the head assembly and bulb. A liquid is contained in the bulb and it is susceptible to temperature variations that cause the metal diaphragm to expand and contract thereby operating the thermostat.
If the diaphragm is not properly age hardened, the thermostat will not operate precisely at higher temperatures. Thus, it is important that the diaphragm be age hardened to enable the thermostats to operate accurately.